In knitting machines, for instance, the needle drive requires constant lubrication, which is equally true for the needle guide in the needle bed or needle cylinder, and so forth. Yet satisfactory, regular lubrication is extremely important, precisely in modern high-speed knitting machines. The lubricating stations must be reliably supplied with oil. As a rule, failure of the lubrication leads to increased water and early failure of the knitting machine. On the other hand, the lubrication must be done in a thrifty way. It is counterproductive to supply too much oil to the lubricating stations. Such knitting machines are therefore often equipped with so-called pressure oilers or pressure oil lubricating systems, which feed oil under pressure from a central point to the individual lubricating stations via suitable lines.
A lubricating device for this purpose, known for instance from European Patent Disclosure EP 0 499 810 B1, permits reliable, metered lubrication of a plurality of lubricating stations. The lubricating device has a lubricant container in which a piston pump is accommodated. The output of the piston pump is connected to a motor-drive distributor valve, so that the pump outlet can be connected to one lubricant line at a time, selected from a group of lubricant lines.
It is an object of the invention to create a simplified lubricating device. It is another object of the invention to create an improved method of lubrication.
These and other objects are attained in accordance with one aspect of the invention directed to a lubricating device comprising a distributor device with which lubricant furnished by a pump is diverted to selected lines and can thus be delivered to selected lubricating stations. The distributor device and the pump device are combined into one unit. Combining the distributor device and the pump device into a unit makes for a considerably simpler design of the lubricating device. The triggering of the lubricating device can be simplified as well.
The pump device is embodied as a piston pump and has a piston that is axially displaceable in a cylinder. Together with the cylinder, this piston serves as a pumping element. The cylinder and the piston are also embodied as a control element. To that end, the piston is rotatably supported in the cylinder and is provided with control faces or conduits, with which control slots or outlets disposed in the cylinder are associated. The piston can be provided on its jacket face with at least one control conduit that is embodied in such a way that by suitable rotary positioning of the piston, it can be brought into coincidence with at least one of the outlet conduits at a time. If needed, the arrangement can also be made such that the control conduit can be switched into coincidence with a plurality of outlet conduits. The control conduit and the outlet conduits are disposed such that the work chamber, defined by the piston and the cylinder, communicates with whichever outlet conduit has been selected, over the entire stroke of the piston. In this way, all the oil volume positively displaced by the piston can be pumped into the outlet conduit. The piston pump embodied in this way is both a pump device and distributor device at one and the same time.
The pump device and the distributor device can be connected to a drive device that effects the rotation and displacement of the piston. This displacement motion is a pumping motion, so that the displacement drive forms a pump drive. If no displacement motion occurs, the rotary motion of the piston causes no change in volume in the cylinder, and as a result, only the blocking or uncovering of outlet conduits is controlled by the rotary motion. Thus the rotary drive is a distributor drive, and the piston is a control slide. The pumping and switchover can thus each be effected independently, by rotating and displacing the piston. This can be done by means of separate drive devices, or by a combined drive device that is capable of generating both a rotary and a displacement motion.
For rotating the piston, a stepping motor is preferably used, which generates a desired rotary positioning motion. Rotary positions to be taken for selecting an outlet conduit and thus for activating a lubricating station are simple to attain with a stepping motor. However, the displacement motion of the piston can be derived from this stepping motor as well. To that end, the piston is preferably connected to the stepping motor or other kind of control motor via a coupling, which initially allows a set or adjustable rotary play, and the relative rotation within the rotary play is converted by a gear means into the desired linear motion.
The rotary angle of the rotary play can be utilized to generate a linear motion. To that end, the piston is preferably connected to a locking device, which keeps the piston nonrotatable in arbitrary or selected rotary positions, but without blocking its axial displacement. By way of example, this locking device can be formed by a locking wheel, which can be brought into and out of engagement with a locking member. This is preferably done by means of a suitable radial motion of the locking member, for instance by means of a pull magnet. If the piston is held in a manner fixed against relative rotation, then a rotation of the stepping motor within the context of the rotary play of the coupling device is possible. The displacement device is now preferably formed by a gear, which converts this relative rotation between the piston and the rotator device into a linear motion of the piston.
In an especially durable, simple embodiment, the locking wheel is embodied as a ratchet wheel. The locking element then acts as a pawl, which allows a rotation of the locking wheel in a selected direction. The pawl can also be releasable, for instance by a lifting magnet, to allow rotation of the locking wheel in the other direction. Such an arrangement allows normal operation of the lubricating device with only a very few actuations of the lifting magnet, used by way of example, for releasing and locking the paw. Even if simple, inexpensive lifting magnets are used, this makes a long service life possible.
The gear can be formed by two threaded elements meshing with one another. The pitch of the thread of the threaded elements is dimensioned such that by the relative rotation between the piston and the control motor, within the context of the rotary play of the coupling device, one complete piston stroke is executed. The piston can be moved back and forth by rotating the control motor forward and in reverse.
As needed, still other devices can serve as the gear means. For instance, it may be expedient to provide a cam drive, which enables a reciprocating motion of the piston upon rotation of the rotary drive in a single specified direction. Such a cam drive can be formed by an undulating annular groove provided in the wall of a bush, in which groove a radially extending pin or prong runs, driven by the control motor.
The gear that generates the linear motion is preferably prestressed. This can for instance be accomplished by means of a magnet that keeps flanks of the gear that slide past one another in contact with one another. This is advantageous particularly with a view to correct metering of the lubricant. If the drive reverses its rotary direction, for instance to change from a forward piston stroke to a reverse piston stroke, then the turning points are precisely defined, and incorrect metering is avoided.
The outlet conduits leading out of the cylinder and one inlet conduit are each preferably provided with check valves. The pump device thus makes do without further control means. The check valves are preferably automatic valves, controlled by the differential pressure applied. No other valve control arrangements are needed.
For monitoring proper operation of the lubricating device, a sensor device that detects and monitors the reciprocating motion of the piston can be advantageous. It may suffice to monitor whether the piston attains a certain stroke or not. For instance, if one lubricating conduit is stopped up, the piston is unable to pump any lubricant into this conduit and is accordingly blocked. It fails to reach the switching point of the sensor device, and the sensor device detects this and turns off the affected machine.
Another aspect of the invention is directed to a method for the lubrication of lubricating stations of a machine by means of at least one pump via lines. Lubricant is pumped discontinuously by the pump to the lubricating stations via the lines. For lubricant supply to one or more lubricating stations, the applicable line or lines are subjected by the pump to a pressure that fluctuates over time. Regardless of the specific design of the pump device and distributor devices in attached lines, and regardless of how many lubricating stations are connected, it is expedient for the pump pressure to be modulated during individual lubricating pulses. If a stepping motor is used to drive the pump, its individual steps can be converted into micropumping pulses, whose train forms a lubricating pulse. The intervals between individual micropumping pulses are expediently dimensioned such that the pressure in the lines does not drop below a minimum limit value. The minimum pressure is preferably somewhat less than the requisite injection pressure for the connected nozzles. It suffices to keep any resilience (elasticity) of the lines under initial stress. This makes it possible either to meter especially small quantities of lubricant, or to prolong the lubricating process.